1. Field of the Invention
The present invention relates to a position controller that causes a feedback position signal to follow a position command.
2. Description of Related Art
When a position controller uses a motor to control driving of a machine, the position controller provides a P-PI (Proportional-Proportional-Integral) minor loop control system which carries out speed control with PI (Proportional-Integral) control by feeding back a rotation speed of the motor, and position control with P (Proportional) control by feeding back a rotation position of the motor.
The position controller improves a response characteristic of a speed control loop by increasing the gain of the PI control of the speed control, and then improves a follow-up characteristic to a position command and a suppression characteristic to a disturbance by increasing a gain of the P control of the position control.
The control system used herein always involves a time delay of calculation and a phase delay of a current loop. Hence, in order to cut high-frequency noise, mechanical vibration, etc., it is necessary to additionally provide an element (delay element) that generates a phase delay, such as a low-pass filter or a notch filter. The position controller having the phase delay of the delay element, however, cannot increase the gain of the PI control of the speed control, resulting in the follow-up characteristic for the position command and the suppression characteristic for the disturbance being poor.
For example, in Japanese Unexamined Patent Application Publication No. 2003-33066, an observer that can compensate the phase delay of the delay element is used, so as to improve the follow-up characteristic for the position command and the suppression characteristic for the disturbance.